CHEMICAL GRAFTING OF TIN ALKYL COMPLEXES ON THE EXTERNAL SURFACE OF MORDENITE - A METHOD FOR CONTROLLING THE SIZE OF THE PORE ENTRANCES OF ZEOLITES

The tetra(alkyl)tin complexes SnR4 (R = Me, Et, i-Pr, Ph or cyclohexyl) and hydridotris(butyl)tin (Bu3SnH) react with the OH groups of the external surface of H-mordenite under the same experimental conditions as silica. For R = Bu, the formation of [GRAPHICS] as the major surface complex could be deduced from the C-13 and Sn-119 magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra. The adsorption properties of these modified mordenites are considerably affected by the presence of the grafted complexes, in a way which is dependent on the nature of the alkyl ligands around Sn. When modified by grafted SnMe3 [2.3% (w/w) Sn], mordenite adsorbs n-hexane, 2-methylpentane at a lower rate, small amounts of 2,3-dimethylbutane (after 16 h) and no significant amounts of 2,2,4-trimethylpentane. All these results can be explained by the restriction of the size of the pore entrances by the grafted organometallic fragments, allowing, in some cases, the separation of mono- and dibranched hydrocarbons.